1. Field of the Invention
The present invention relates to an acoustic apparatus using a resonator as an acoustic radiation member.
2. Description of the Prior Art
In an acoustic apparatus, a resonance phenomenon is utilized in a variety of forms. FIGS. 29 to 32 show typical prior art examples in which the resonance phenomenon are utilized.
In a first prior art shown in FIG. 29, a resonance cabinet 1 is partitioned into two chambers, i.e., A and B chambers, by a partition wall 2. A dynamic electro-acoustic transducer (dynamic speaker) 3 serving as a vibrator is attached to a hole of the partition wall 2. Opening ducts 4a and 4b are respectively provided to the A and B chambers, and resonance acoustic waves are externally radiated from these ducts, as indicated by arrows. The A and B chambers respectively have resonance frequencies f.sub.oa (Hz) and f.sub.ob (Hz) determined by the volumes of cavities (i.e. the volumes of chambers A and B), the dimensions of the opening ducts 4a and 4b, and the like. Therefore, when the speaker 3 is driven by an amplifier (not shown), a resonance phenomenon occurs by the vibration of a diaphragm, and an output energy at that time has maximum values near the above-mentioned resonance frequencies. As a result, the resonance acoustic waves having sound pressure-frequency characteristics illustrated in FIG. 30 can be obtained.
In a second prior art shown in FIG. 31, a dynamic electro-acoustic transducer (speaker) 6 serving as a vibrator is attached to a resonance chamber 5' defined by a cabinet 5, and an opening 7 for externally radiating resonance acoustic wave is formed in the chamber 5'. Another dynamic electro-acoustic transducer (speaker) 8 is separately provided to the cabinet 5, so that an acoustic wave is directly radiated therefrom In this acoustic apparatus, when the speaker 6 is driven by an amplifier (not shown), a resonance phenomenon occurs in the resonance chamber 5' due to the vibration of a diaphragm of the speaker 6. Therefore, acoustic reproduction illustrated in FIG. 32 is made from the opening 7 to have a peak sound pressure near a resonance frequency f.sub.o inherent to the resonance chamber 5'.
However, according to conventional acoustic apparatuses, the vibrator undesirably causes a decrease in resonance Q value of the resonator serving as an acoustic radiation member. This is because the speaker as the vibrator has an inherent internal impedance Z.sub.v, and the internal impedance damps the resonance of the resonator. In this manner, if the resonance Q value is low, radiation power of the resonance acoustic wave is inevitably low and the presence of the resonator in the acoustic apparatus is meaningless.
If the resonance frequency is decreased while rendering the resonator compact, the opening duct must be elongated. Accordngly, the acoustic resistance (mechanical resistance) of the-opening duct is inevitably increased, and the resonance Q value is decreased further For this reason, the acoustic radiation power is further decreased due to a decrease in resonance Q value, and the acoustic apparatus is not suitable for a practical use.
As a result, neither of the conventional apparatuses shown in FIGS. 29 and 31 have sufficient acoustic radiation power. If a certain level of power is to be maintained, the cabinet becomes extremely large.